you will have to show us how you use it, and what incorrect
results you get on what data.

If I have the following data: Cell A1 = -4, and cell B1 = ABS(A1) = 4.

In VBA, Range("B1").value = Abs(Range("A1").value) will give you the
same result.

Worksheetfunction.abs(expression) is not a supported function. For more
information, also type in abs  in the VBE search box, look at the Abs
function search result for possible errors.

It works OK for me. Show us the formula  and the input and we might be able to
help.

You were expecting it to do:

If input > 0 result = input
If input = 0 result = 0
If input < 0 result = -input ?